There are many existing network services that require real-time delivery of multimedia data over a network. For example, packet-based telephony service, such as voice-over-IP (“VoIP”) telephony, typically includes the real-time delivery of voice, and possibly other multimedia data types such as video data, on a network using RTP (Real-Time Transport Protocol) to exchange information required to control the delivery of data. The perceived quality of VoIP telephony service can be determined by various parameters affecting the real-time delivery of the data over the network, such as network conditions, and the network resources allocated for the delivery of the data.